This invention is generally directed to squaraine compositions of matter, and the incorporation thereof into layered photoresponsive imaging members. More specifically, the present invention encompasses layered photoresponsive imaging members having incorporated therein as photogenerating pigments the unsymmetrical squaraine compounds illustrated hereinafter. Accordingly, in one embodiment of the present invention the photoresponsive imaging member, which is sensitive to visible and/or infrared wavelengths, is comprised of a photoconductive or photogenerating layer containing the unsymmetrical squaraine compounds illustrated hereinafter, and an aryl amine hole transport layer. Moreover, included within the scope of the present invention are imaging members which are responsive to visible light, and infrared illumination needed for laser printing, which members comprise, for example, in addition to an unsymmetrical squaraine photoconductive layer and an aryl amine hole transport layer, a photogenerating layer.
Numerous different xerographic photoconductive members are known including, for example, a homogeneous layer of a single material such as vitreous selenium, or a composite layered device with a dispersion of a photoconductive composition. An example of one type of composite xerographic photoconductive member is described in U.S. Pat. No. 3,121,006 wherein there is disclosed finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. One member comprises, coated on a paper backing, a binder layer with particles of zinc oxide uniformly dispersed therein. The binder materials disclosed in this patent comprise a material such as polycarbonate resins, polyester resins, and polyamide resins, which are incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. As a result the photoconductive particles must be in a substantially contiguous particle to particle contact throughout the layer to permit charge dissipation required for a cyclic operation. Accordingly, a relatively high concentration, about 50 percent by volume, of photoconductive material is usually necessary to obtain sufficient photoconductor particle to particle contact for rapid discharge. This high photoconductive loading can destroy the physical continuity of the resinous binder, and thus significantly reduce the mechanical properties thereof. There are also known photoreceptors comprised of inorganic or organic materials wherein the charge carrier generating, and charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, layered photoreceptor materials are disclosed in the prior art which include an overcoating layer of an electrically insulating polymeric material.
Recently, there has been disclosed specific layered photoresponsive devices comprised of separate generating and transport layers, reference U.S. Pat. No. 4,265,990; and overcoated photoresponsive members with a hole injecting layer, a hole transport layer, a photogenerating layer, and a top coating of an insulating organic resin, reference U.S. Pat. No. 4,251,612. The disclosures of each of these patents are totally incorporated herein by reference.
Many other patents are in existence describing layered photoresponsive layered devices with generating substances, such as U.S. Pat. No. 3,041,167, which discloses an overcoated imaging member containing a conductive substrate, a photoconductive layer, and an overcoating layer of an electrically insulating polymeric material. This member is utilized in an electrophotographic copying method by, for example, initially charging with an electrostatic potential of a first polarity, imagewise exposing, and subsequently effecting development thereof. Prior to each succeeding imaging cycle, the member can be charged with an electrostatic charge of a second opposite polarity. Sufficient additional charges of the second polarity are applied so as to create across the member a net electrical field. Simultaneously, mobile charges of the first polarity are created in the photoconductive layer by applying an electrical potential to the substrate. The imaging potential which is developed to form the visible image is present across the photoconductive layer and the overcoating layer.
There is also disclosed in Belgian Pat. No. 763,540 an electrophotographic member having at least two electrically operative layers, the first comprising a photoconductive layer which is capable of photogenerating charge carriers, and injecting these carriers into a continuous active layer containing an organic transporting material which is substantially non-absorbing in the spectral region of intended use, and permits the injection of photogenerated holes from the photoconductive layer. Additionally, there is disclosed in U.S. Pat. No. 3,041,116 a photoconductive material with a transparent plastic material overcoated on a layer of vitreous selenium present on a substrate.
Furthermore, there is disclosed in U.S. Pat. Nos. 4,232,102 and 4,233,383 photoresponsive imaging members comprised of trigonal selenium doped with sodium carbonate, sodium selenite, and trigonal selenium doped with barium carbonate; and barium selenite or mixtures thereof. Moreover, there is disclosed in U.S. Pat. No. 3,824,099 certain photosensitive hydroxy squaraine compositions. According to the disclosure of this patent, the squaraine compositions are photosensitive in normal electrostatographic imaging systems.
Also, there is illustrated in U.S. Pat. No. 4,415,639, the disclosure of which is totally incorporated herein by reference, the use of hydroxy squaraines as a photoconductive layer in an infrared sensitive photoresponsive device. More specifically, there is described in this patent an improved photoresponsive device comprised of a substrate, a hole blocking layer, an optional adhesive interfacial layer, an inorganic photogenerating layer, a hydroxy squaraine photoconductive composition capable of enhancing or reducing the intrinsic properties of the photogenerating layer, and a hole transport layer.
Additionally, there is disclosed in U.S. Pat. No. 4,471,041, the disclosure of which is totally incorporated herein by reference, the use of novel julolidinyl squaraine compositions as photoconductive substances in photoresponsive devices which are sensitive to infrared light, and/or visible illumination. As indicated in the above-mentioned patent, the improved photoresponsive device in one embodiment is comprised of a supporting substrate, a hole blocking layer, an optional adhesive interfacial layer, an inorganic photogenerating layer, a photoconducting composition capable of enhancing or reducing the intrinsic properties of the photogenerating layer, which composition is comprised of the novel julolidinyl squaraine compositions disclosed therein, and a hole transport layer.
There is further disclosed in U.S. Pat. No. 4,486,520 photoresponsive imaging members with photogenerating layers of certain fluorinated squaraine compositions. Examples of specific fluorinated squaraines disclosed include bis(4-dimethylamino-2-fluorophenyl)squaraine, bis(4-[N,N,diethylamino-2-fluorophenyl])squaraine, bis(4-[N-methyl-N-ethyl-2-fluoroaniline])squaraine, bis(4-[N,N-dibenzyl-2-fluoroaniline)squaraine, bis(4-[N-methyl-N-benzyl-2-fluoroaniline])squaraine, and bis(4-[N-ethyl-N-benzyl-2-fluoroaniline])squaraine. Other useful fluorinated squaraine compositions include bis(4-[N,N,-di(4-chlorophenylmethyl)-2-fluorophenyl])squaraine, bis(4-[N-methyl-N-(4-chlorophenylmethyl)-2-fluorophenyl])squaraine, and bis(4-[N-benzyl-N-(-chlorophenylmethyl)-2-fluorophenyl])squaraine. The disclosure of this patent is totally incorporated herein by reference.
There is also illustrated in a copending application U.S. Ser. No. 557,795, now U.S. Pat. No. 4,521,621, entitled Novel Squaraine Systems, the disclosure of which is totally incorporated herein by reference, photoresponsive imaging members with unsymmetrical squaraines similar to those of the present application. More specifically, there is disclosed in this patent application a process for synthesizing an unsymmetrical squaraine comprising forming a mixture of squaric acid, a primary alcohol having a boiling point between 150.degree. C. and about 190.degree. C., a first tertiary amine having the formula: ##STR2## and a second tertiary amine having the formula: ##STR3## wherein R.sub.1, R.sub.2, R.sub.5 and R.sub.6 are independently selected from the group consisting of alkyl radicals having from 1 to 4 carbon atoms, phenyl radicals and radicals having the formula: ##STR4## and R.sub.3, R.sub.4, R.sub.7 and R.sub.8 are independently selected from the group consisting of H, CH.sub.3, CH.sub.2 CH.sub.3, CF.sub.3, F, Cl, Br, and COOH wherein at least one of R.sub.3 and R.sub.4 are different than R.sub.7 and R.sub.8 if R.sub.7 and R.sub.8 are located on the same relative position on the aromatic ring as R.sub.3 and R.sub.4 ; and wherein R.sub.9 is selected from the group consisting of H, alkyl radicals having from 1 to 4 carbon atoms, F, Cl, Br, COOH, CN and CF.sub.3 ; and heating the mixture at a temperature below the boiling points of the alcohol, the first tertiary amine and the second tertiary amine.
Furthermore, there is disclosed in copending application U.S. Ser. No. 650,380, now U.S. Pat. No. 4,559,286, the disclosure of which is totally incorporated herein by reference, entitled Processes for the Preparation of Mixed Squaraine Compositions, other unsymmetrical squaraines. Specifically, there is illustrated in this application a mixed squaraine composition comprised of the following three components ##STR5## Nevertheless, there continues to be a need for new squaraine compounds which are useful in photoconductive imaging members. Also, there continues to be a need for photoresponsive imaging members comprised of unsymmetrical squaraine compounds. Further, there is a need for layered unsymmetrical squaraine photoresponsive imaging members that are sensitive to a broad range of wavelengths, and more specifically are sensitive to infrared light and visible light thereby permitting their use in a number of imaging and printing systems. Moreover, there continues to be a need for imaging members with unsymmetrical squaraine compounds which can be repeatedly used in a number of imaging cycles without deterioration thereof from the machine environment or surrounding conditions. There also continues to be a need for specific unsymmetrical squaraine photogenerating pigments with a hydroxy substituent thereon, which simultaneously possess higher photosensitivity than closely related squaraines, low dark decay properties, and high charge acceptance values thereby permitting images of excellent resolution with minimum background deposits to be obtained. Another need resides in providing layered photoresponsive imaging members with unsymmetrical squaraine compounds, photogenerating pigments, and aryl amine hole transport molecules.